Telephone line circuit



2 Sheets-Sheet 1 A V I v 36L 4 T m N N E R MD. PVL m m mQEmEEE m m m M 2.2 7 25 m h v I -20 $6 M M. E. GRIFFINS TELEPHONE LINE CIRCUIT Filed Oct. 5, 1940 om. v 0. mobmzzou v EL Mm NM. om. mwnzz m2 8. x2: mebwzzou E2; #0. mEBzzS OF Eo wZj 4:0 NZ: ZONE March 30, 1943.

March 30, 1943. M. E. GRIFFINS TELEPHONE LINE CIRCUIT Filed Oct. 5, 1940 2 Sheets-Sheet 2 man vow

INVENTOR MORRIS E GRIFFINS BY ATTORNEYS Patented Mar. 30, 194 3 PATENT" FFlCE TELEPHONE LINE cmcm'r Morris E. Griffins, Riverside, 111., assignor to Asso ciated Electric Laboratories, Inc., Chicago, 111.,

a corporation of Delaware Application October 5, 1940, Serial No. 359,827

11. Claims.

The present invention relates tolinecircuits for automatic telephone systems and more particularly to improved line circuits of the general character disclosed in U. S. Patent No. 2,199,543, Clarence E. Lomax", granted May 7, 1940. In the Lomax patent, on improved telephone line circuit for a subscriber line of the party type is disclosed, which is so connected and arranged that associatedautomatic switching apparatus is controllable to render by way of the subscriber line both calling and called services and also revertingcall service, in spite of the fact that the line circuit comprises only two relays, a line relay and a cut-o ff relay.

While this .line circuit is entirely satisfactory in operation and productive of a considerable reduction in manufacturing costs over conventional line circuits, it, in turn, is somewhat more ex-' pensive, to manufacture than, is desirable, due primarily to the provision of a mechanical interlock between the line relay and the cutoff relay embodied therein. i K Accordingly, it is an object of the present invention to provide an improved telephone line circuit of the type described which comprises only a line relay and a cutoff relay, and which rquires no mechanical interlock between the line relay and the cutoif relay.

Another object of the invention is toprovide a telephone hne circuit of the type described which embodies an improved'and exceedingly simple circuit network.

The objects set forth above are attained in ac cordance with the present invention by providing a line circuit adapted for use in a telephone system "including a subscriber line of the party type and automatic switching apparatus having eluding in series the first winding and a second winding of the cutofi felay. The control network is so connected and arranged that the first, second and third operating circuits are selectively controlled incident to' rendering calling and called services over the subscriber line; while the fourth operating circuit is controlled incident to rendering reverting call service over the subthe following specification taken in connection with the accompanying drawings, in which Eigures 1 and 2 taken together illustrate diagrammatically a telephone system including a line circuit embodying the presentinvention.

Referring ,now--more particularly to Figs. 1

and 2 of the drawings, the telephone system;

there. illustrated. comprises an exchange having a plurality of subscriber lines, including the subscriber lines I50 and I60, terminating thereat and provided with .a plurality of finder-connector links, including the-link 100, for setting up conaccess to the subscriber line; which hne circuitselectively operating the line relay and the cutofi relay, and control circuits for the switching ap- .paratus governed by the line relay and the cutoff relay, whereby the switching apparatus is l selectively controllable to render the substations on the subscriber line both calling and called services and also reverting call service. i

,nections between the various subscriber lines. Also, a distributor 103 is provided, for assigning 1 line when a reverting call is initiated thereon.v

More specifically, the exchange has an ultimate capacity of-one hundred lines and the number of-links is determined by the amount of traflic More particularly, the control network for the\ line relay and the cutofi relay comprises a first operating circuit including a first winding of the line relay, a second operating circuit including which the exchange is required to handle, usually ten links being adequate to render satisfactory service.

, Each of the links may be identical to the link I00 which comprises a finder I Ill and a connector 102, each having access to each subscriber line a in the system. The finder and the connector included in'the link may be of any of a number of well-known types. However, it is. preferable that both the finder and the connector include a switching mechanism of the Strowger type and the usual control apparatus therefor, the wipers of the switching mechanism included in the finder III being illustrated at I80, I8I and I82, and the wipers of' the switching mechanism included in the connector I02 being illustrated at I83, I84 and. I85. Also,. the connector I02 comprises impulse-responsive apparatus of any desired type "for projecting coderinging current over an idle called subscriber line after it hasbeen seized by the switching mechanism included therein, which is'so connected and arranged that a divided ringing circuit may be employed in the system. The distributor I03 may be of any of a well-known number of types. However, it is preferable that the distributor I03 is of the preselective type such that an idle link is selected to be assigned to the use of a calling subscriber line prior to the initiation of a call on the subscriber line.

At least a number of the subscriber lines terminating at the exchange are of the party type,

the subscriber lines, I50 and I60 being party subscriber lines, each serving a number of substations respectively including the substations A, B and C, D. Each of the substations is provided with a telephone instrument, a dial mechanism and a ringer. The substations associated with each party subscriber line are arranged in two groups the ringer at each substation in the first group being connected between one line conductor of the subscriber line and ground, and the ringer at each substation in the-second group being connected between the other line conductor of the subscriber line and ground, wherevby a divided ring ng circuit is employed in the' system. A line circuit is individually associated with each subscriber line in the system, the line -cir-,

, comprises-two minor switches 280 and 290, a line relay R230, a hold relay R240, two transfer relays R200 and R2I0 a ring cutofl. relay R255, a switch-through relay R220, 'twocontrol relays 'R2I0 and R250, the control and controlled circuits therefor, and a transformer 20I. The minor switch 280 comprises two rotary wipers 283 and 285 provided with individually associated contact banks 284 and 286. respectively, a rotary magnet-M230 for driving the wipers noted, and a release magnet M231 for releasing the wipers noted and for causing them to be returned to their normal positions. Also, a set of switch springs S234 is individually associated with the minor switch 280 and controlled by the operation of thewipers thereof away from their normal- Similarly, the minor switch 290 compositions. prises two'rotary wipers 293 and 295 provided with individually associated contact banks 294 and 290, res ctively, a rotary magnet M238 for driving the ipers noted, and a release magnet M239 for releasing the wipers noted and for causing themto be returned to their normal positions; Also, a set of switch springs S235 isindividually associated with the minor switch 280 and controlled by the operation of the wipers is connected and arrahged to project code rin' ging current over a calling subscriber line by way of the trunk I10 when a connection is established therebetween by way of an operated one of the links, in such a manner that a divided ringing circuit is employed in the system.

The connection'and arrangement of the system will best be understood from a consideration of the operation of the apparatus incorporated therein to set up the diiferent connections between the various subscriber lines.

A call which is to be extended from the substation A to the substation C is first initiated at the substation A by removing the receiver of the telephone instrument thereat from its associated switchhook, thereby to complete a bridge path at the telephone instrument at the substation A between the line conductors CI5I and CI52 of the subscriber line I50 extending thereto. When this bridge path between the line conductors of the subscriber line I50 is completed, a bridge circuit is completed for energizing the upper wind- .ing of the line-relay RI20 in the line circuit I04 individually associated with the subscriber line I50. This bridg circuit extends from ground by way of the contacts II5 to the line conductor station A. When thus energized, the line relay RI20 operates to complete, at the contacts I23, a priming circuit for energizing in series the upper and lower windings of the cutofl relay RI II, this circuit extending from ground by way of the lower winding of RI I0, the contacts I23, the resistor I28 and the upper winding of- RI I0 to battery. When this priming circuit is thus completed the cutoif relay RI I0 does not operate due to the high series resistance of the resistor I28. Also, the line relay RI20 completes, at the contacts I2I, a path for applying battery potential to the control conductor CI53 of the subscriber line I50, this path extending from battery by way of the upper winding of the cutofl. relay,

RI I0, the lower winding of the line relay RI20 and the contacts IZI to the control conductor CI53. This application of battery potential'to the control conductor CI53 ofthe subscriber line I50 marks the rotary position of the contact set in the level in the contact bank of the Strowger mechanism included in the finder IOI, wherein the calling subscriber line I50 terminates. 'Fl-. nally, the line relay RI20 completes, at the contacts I21, an obvious path for applying ground potential to the start conductor CI extending into the distributor I03. ground potential to the start. conductor CI90 initiates the'operation of the distributor I03 and causes the distributor to operate and assign the previously selected idle link to the use of the calling subscriber line I50. Assuming that the link I00 illustrated is assigned by the distributor I03 at this time, the distributor also marks with ground potential by way of the conductor CH3 the level in the-contact bank of the Strowger ,mechanism included in the finder IOI, wherein terminates. This Strowger mechanism then op- This application of 2,314,933 crates to move the wipers thereof in the rotary direction to the rotary position of the contact set,

'wherein, the callingsubscriber line I50 terminates, at which time the wipers I80 and I82 thereof engage the contacts terminating the line conductors CI and CI52, respectively, of the subscriber line I50, and the wiper I8I thereof a circuit for energizing a relay in the finder IOI, thereby to cause the last-mentioned relay to operate and arrest further operation of the Strowger mechanism included therein; whereupon apparatus in the finder IOI operates to complete a path for applying ground potential to the wiper I8I. This application of ground'potential to the wiper I 8| completes a circuit for energizing in series the lower winding of the line relay RI and the upper winding of the cutoff relay RI I0, this circuit extending from the grounded wiper I8I by way of CI53, the contacts I2I,-the lower winding of RI20 and the upper winding of RI I0 to battery. Also, this application of ground potential to the wiper I8I completes a path for applying ground potential to the control conductor CI54 of the subscriber line I'50extending to the contact banks of the Strowger mechanisms included in the connectors of the links having access thereto, thereby to mark the subscriber line I50 as busy to the connectors of these links. This path extends from the grounded wiper I8I by way of CI53, the contacts I2I and I to the control conductor CI 54.

When the lower winding of the line relay RI20 I and the upper winding of the cutoff relay RI I0 are thus energized, theline relay RI 20 is held 0p-' erated and the cutoff relay RI I0 operates. Upon operating, the cutofi relay RI I0 interrupts, at the contacts I I I and I I5, points in the original bridge circuit for energizing the upper winding of the line relay RI20,-thereby to free the line conductors CI5I and CI52 of the subscriber line I50 of empedance' elements. Finally, the cutoff relay RI I0 interrupts, at the contacts H6, the previously mentioned path for applying ground potential to the start conductor CI90 extending into the distributor I03. When ground potential is removed from the start. conductor CI90 the distributor I03. operates to preselect an idle link in the group of links to be assigned to the use of the next calling subscriber line. Whenihe finder the connector I02 operates in response to a first series of impulses in order to cause the wipers I83, I84 and I85 of the Strowger mechanism included therein to be moved tin the vertical direction to the level in the contact bank thereof,

wherein the called subscriber line I60 is termi-.

n'ated. The subscriber at the substation A then dials the second digit of the directory number of the called substation C at the dial mechanism thereat, thereby to transmit a second series of impulses by way of the previously mentioned loop til circuit to the connector I02 in order to cause th wipers noted of the Strowger mechanism in-.

cluded therein to be moved in the rotary direction to the position of the contact set in the contact bank thereof, wherein the called subscriber line I60 is terminated. The subscriber at the substation A then dials the third digit of the directory number of the called substation C at the dial mechanism thereat, thereby to transmit a third series of impulses by way of the previously mentioned loop circuit to the connector I02 in order tocause the connector to select a corre-, sponding code ringing current to be projected over the called subscriber line I60 in the event it is idle.

scriber line I60. At this time, ground potential appears upon thecontrol conductor CI in the event the called subscriber line I60 is busy On the other hand, battery potential appears upon the control conductor C I 64 in the event the called subscriber line I60 is idle.

Assuming that the called subscriber line I00 is busy, ground potentiaf. derived in the line circuit I05 individually associated therewith appears upon the control conductor CI64 thereof, thereby to complete a path for energizing a busy relay included in the connector I02, which busy relay operates to cause busy tone current to be returned over the previously mentioned loop circuit including the calling subscriber line I extending to the substation A, in the usual manner. The production of busy'tone in the receiver of the telephone instrument at the calling substation A indicates to the subscriber thereat' that the desired connection cannot immediately be had due to the busy condition of the called subscriber line I60. The subscriber at the calling substation A then releases the operated link I00 and the line circuit I04 by replacing the receiver of the telephone instrument at'the substation A upon its associated switchhook. The exact manner inv pathfor applying battery potential to the control conductor CI64 of the subscriber line I ex tends from battery by way of the upper .winding of the cutofi relay RI40, the lower windingpf the line relay RI30, and the contacts I43 to the con trol conductor CI64. This application of battery potential to the control conductor CI04 completes a path for short-circuiting the busy relay included in the connector I02, thereby to cause the connector I02 to operate and project ringing current of the previously selected cede over the called subscriber line I60; whereby the ringer at the called substation C is operated in a characteristic manner. This charact ristic operation cf the ringer at the called substation C indicates to the subscriber thereat that the substation C is the called substation. Also, a switchthrough relay in the connector I02 operates to apply direct ground potential to the wiper I84 of the Strowger mechanism therein. This application of ground potential to the wiper I04 completes a circuit for 1 1 energizing in series the lower winding of the line relay RI" and the upper winding of the cutoff asieoss relay RI, this circuit extending from the grounded wiper I06 by way of CI, the contacts".

' tors CIBI and CI" 01' the subscriber line I of impedance elements. Also, the cutoff relay RIlII interrupts, at the contacts I46, a point in an ob.-

yvious path for app ying ground potential to the start conductor CI90. Upon operating, the line relay RI30 completes, at the contacts I33, a priming circuit for energizing in series the upper and lower windings of the'cutofi relay RI40, this circuit extending from ground by way of the lower winding of Rl40, the'contacts I33, the resistor I38 and the upper winding of-RI40 to battery. Finally, the line relay RI30 completes, at the contacts I3I and I35, a connection between the grounded control conductor CI64 of the subscriber line I60 and the control conductor CI63 or the subscriber line I60 extending to the contact banks 01' the Strowger mechanisms included in the finders of the links having access thereto, thereby to mark the subscriber line. I60 as busy to the finders of theselinks, this path extending from the grounded control conductor CI by way of the contacts I35 and I3I to the control conductor CI53. The subscriber at the substatiorf C then answers the call by removing the receiver of the conductor cm oi. the subscriber line m, there:

by to mark the subscriber line I50 as idle to the Strowger mechanisms included in the connectors 01 the links having access thereto. This path extends from battery by way of the upper winding of the cutoff relay RI I0, the lower winding of the line relay Ri and the contacts III to the control conductor CI" of the subscriber line I50. At this time, the line circuit I04 is completely released. I Also, when the link I00 is released, ground potenti-al therein is removed from the wiper I,

- thereby to interrupt the previously traced circuit for energizing in series the lower winding of the line relay RI30 and the upper winding of the cutoil. relay RI40, thereby to cause the line relay RI30 to restore immediately and the cutofl relay.

' RIM to restoreshortly thereafter, the cutofl. relay Rlle being rendered slow to release while the line relay RI is operated, due to the completed priming circuit for energizing in series theupper and lower windings thereof, as, previously noted. Upon restoring, the cutofl relay RI prepares, at the contacts I and I45, points in the previously mentioned bridge circuit; including the subscriber line I60, for energizing the'upper winding of the line relay RI30. Also, upon restoring the cutoff relay RI40 completes, at the contacts I43, the

' previously traced path for applying battery potential to the control conductor CI54 oi the subscriber line I60, thereby-to mark the subscriber line I60 as idle to the Strowger mechanisms included in the'connectors or the links having access thereto. At this time, the line circuit I05 is completely telephone instrument thereat from its associated switchhook, when the last subscriber at one of the-substations replaces the receiver of the telephone instrument thereat upon its associated switchhook, the operated link I00 is released in the usual manner, thereby to interrupt the established communication connection extending between the subscriber lines I50 and I50. When the link.I00 is released, ground potential therein released.

In view 01' the-above description of the mode of operation of the apparatus to extend a call from the substation A to. the substation C, it will be understood that the apparatus is operative, in a.

substantially identical manner, to extend a call 'i'rom the substation A to the substation D, from the substation B to the substations C or D, from the substation C to the substations A or B and from the substation D to the substations A 'or B.

A reverting. call which is to be extended from the substation"A,to the substation B is,flrst initiate'd at the substation A by removing the reates in order to cause battery potential to be apis re'moved from the wiper I8I, thereby to interrupt thepreviously traced circuit for energizing in series the lower winding of the line relay RI20 and the upper winding of the cutofl relay RI I0, thereby to cause the line relay RI20 to restore immediately and the cutofl' relay RI l0 to restore shortlythereafter the cutoff relay RIIO being rendered slow to release while the line relay RI20' is operated, due to the completed priming circuit for energizing in series the upper and lower windings thereof, as previously noted. Upon restoring, the cutoff relay RIIO prepares, at the contacts IILand H5, points in the previously traced bridge circuit, including the subscriber line I50, for energizing the upper winding of the line relay RI20. Also, upon restoring; the cutof! relay RI I0 completes, at the contacts I I3, a path for applying battery potential to the control plied to the control conductor CI53 oi the sub scriber line I50 and ground potential to be applied to-the start conductor CH0; and to complete the plained. This application 'of ground potential to the start conductor CI90 causes the distributor I03 to operate and assign a previously selected idle link in the group of links to the use of the calling subscriber line I50, in, the manner previously explained. Assuming that the link I00 illustrated is assigned to the use of the calling subscriber line I50, this application of ground potential to the-start conductor CI 90 and this applicaof the contact set in the contact bank of the tion of battery potential to'the control conductor CI 53 of the subscriber line I 50 marks the, position Strowger mechanism included in the finder IOI,

wherein the subscriber line I50 is terminated;

subscriber at the substation A then dials at the dial mechanism thereat successively two predetermined digits into the connector I02, thereby to cause the connector I02 to operate and select 'thc first trunk line terminating thereat to which an idle reverting call switch is connected. When these two predetermined digits are successively dialed the connector I02 operates as a trunk hunting connector in order to select atrunk line associated with an idle one of the reverting call .switches or to return busy tone current over the loop circuit extending to the calling substation A in the event all of the reverting call switches are busy.- Assuming that .the reverting call switch 200 illustrated is the first idle switch, the con-' nector I02 operates to seize the trunk line I extending thereto. The reverting cail switch 200 is marked as idle or busy, respectively, by the presence of battery or ground potentials upon the control conductor CI12 of the trunk line I10. At this time, the reverting call switch 200 being idle, battery potential appears upon the control conductor C I12 of the trunk line I10, the path for applying battery potential to the control conductor CI12 extending from battery by .way of the resistor 206 and the contacts 21I, MI and 256 to the control conductor CI 12. When the connector I02 selects the trunk line I10, further operation thereof is arrested due to the presence of battery potential upon the control conductor CI12 of the trunk line I10, in the usual manner.

the connector I02, this connector operates to complete a loop circuit between the calling substation A and the line relay R230 in the revertv40 When the trunk line I10 is thus seized by.

CI13 of the trunk line I10, and from battery by way of the upper winding of R230 and the contacts 22I to the line conductor CI1I of the trunk line I10,-the lineconductors CI1I .and CI13 of the-trunk line I10 being connected by way of the operated link I00 to the lineconductors CI5I and CI52, respectively, of the calling subscriber line I50, and the telephone instrument at the substation A being' included in the previously traced bridge path extending between the line conductors CI5I and CI52 of th subscriber line I50.. When thus energized, the line relay R230 operates to complete, at the contacts 23I, an obvious circuit for energizing the winding of the hold relay R240. When thus energized, the hold relay R240 operates to complete, at/the contacts 242, a path for applying ground potential to the control conductor CI12 of the trunk line I10, this path extending from ground by way of the contacts 242 and 256 to the control conductor CI12. This application of ground potential to the control conductor CI12 of the trunk line I10 marks this trunk line as busy to the Strowger mechanisms included in the connector of the links having access thereto and causes the switchthrough relay in the connector I02 to operate.

When the switch-through relay in the connector link I00 is removed from the wipers m and m of the finder and. connector IOI ,and I02, respectively, the link I00 and the lin circuit I04 being retained in their operated positions at this time, due to the application of ground potential to the control conductor CI12 of the trunk line I10 in the reverting call switch 200.

The subscriberat the calling substation A then I dials at the dial mechanism thereat a third digit corresponding to the last digit of the directory .number of the calling substation A, thereby to transmit a series of'impulsesby way 01 the pree viously mentioned 100p circuit to the .line relay R230. The line relay R230 follows the dialed impulses in theusual manner, restoring each time, theloop circuit isinterrupted and operating-each timetheloop circuit is completed. Each time the line-relay R230 restores it interrupts, at

th contacts 23L the previously mentioned circuit for energizing the winding lay R240, and completes, at the contacts 232, a

the control relay-R250 and the rotary magnet tioned circuit extends from ground by way of .the co'ntacts232 and 244 to the contacts 263,

prthe hold recircuit for energizing'in multiple the winding of M236 of the minor switch 280. The last-menway of the contacts 214 and the rotary magnet M236 to battery. The'hold relay, R230 and the control relay R250 being of the slow-to-relcase type, remain operated during impulsing. Each time the circuit for energizing the rotary magnet M236 is completed this magnet operates to drive the wipers 283 and 285 of theminor switch 280 one step in the clockwise direction away from their normal positions. When the wipers noted of the minor switch 280 are drivenaway from their normal positions the set of switch springs S234 is actuated into engagement, thereby to prepare a circuit traced hereinafter for energizing the winding of the transfer relay R210, this circuit being interrupted at this time, at the contacts 25I, by the operated control relay R250. In response to the third digit, the wiper 283 and 285 of the minor switch 280 are driven a number of steps away from their normal positions corresponding to the digit dialed, and into engagement with corresponding contacts in the associated contact banks 284 and 286, respectively.

At the conclusion of the third digit, the line relay R230 reoperates, thereby to interrupt, at the.contacts 232, the previously traced multiple circuit for energizing the winding of the control relay R250 and the rotary magnet M235, whereupon the control relay R250 restores shortly thereafter, and further operation of the rotary magnet M236 is arrested. Upon restoring, the control relay R250 completes, at the contacts 25I, the previously mentioned circuit for energizing the winding of the transfer'relay R210, this circuit extending from groundby way of the set of switch springs S234, the contacts 25! and the winding of R210 to battery. When thus energized, the transfer relay R210 operates to complete, at the contacts 212, an obvious holdv ing circuit for energizing the winding thereof, nd prepares, at the contacts 213, a multiple circuit traced hereinafter for energizing the I02 operates, ground potential in the operated winding of the control relay R250 and the rotary magnet M238 of the minor switch 290.

The subscriber at the calling substation A then number of the called substation B, thereby to tion away from their normal positions.

the wipers noted of the minor switch 288 aretransmit another series of impulses by way of the previously mentioned loop circuit to the line relay R238. The line relay R238 follows the dialed impulses in the usual manner, restoring each time the loop circuit is interrupted and operating each time the loop circuit is completed. Each time the line relay R238 restores it interrupts, at the contacts 23I, the reviously mentioned circuit for energizing the winding of the hold relay R248, and completes, at the contacts 232, the previously mentioned circuit for energizing in multiple the winding of the control relay R258 and the rotary magnet M238 of the minor switch 288. mentioned circuit extends from ground by way of the contacts 232 and 2 to the contact 253, from the contact 253 by way of the winding of R258 to battery; and from the contact 253 by way of the contact 213 and the rotary magnet M238 to battery. Each time the circuit for energizing the rotary magnet M238 is completed, this magnet operates to drive the wipers 293 and 295 of the minor switch 298 one step in the clockwise direc- When driven away from their normal positions, the set of switch springs S235 is actuated, thereby to prepare a circuit traced hereinafter for energizing The last-' the winding of the transfer relay R258, this circuit being interrupted at this time, at the contacts 252, by the operated control relay R258. In 'response to the fourth digit, the wipers 293 and 285 of the minor switch 298 are driven a number of steps away from their normal positions corresponding to the digit dialed, and into engagement with corresponding contacts in the associated contact banks 284 and 285, respectively. At the conclusion of the fourth digit, the line relay R238 reoperates, thereby to interrupt, at the contacts 232, the previously traced circuit for ener izin in multiple the winding of the control relay R258 and the rotary magnet M23;8 in order to cause the control relay R258 to restore shortly thereafter and to arrest further. operation of the rotary magnet M238. Upon restoring, the control relay R258 completes, at the contacts 252, the previously mentioned'circuit for energizing the winding of the transfer relay R258, this circuit extending from ground by way of the set of switch springs S235, the contacts 252 and the winding of R258 to battery. When thus energized, the transfer ,relay R258 operates to'complete, at the contacts winding thereof.

Shortly following the conclusion of the fourth digit dialed at the substantion A, the subscriber thereat replaces the receiver of the telephone instrument thereat upon its associated switchhook, thereby to interrupt the previously mentioned loop circuit for energizing in series the upper and lower windings of the line relay R238, whereupon the latter relay restores. Upon restoring, the line relay R238 completes, at the contacts 232, a circuit for energizing the winding of the control relay R2l8, this circuit extending from ground by way of the contacts 232, 2, 252 and 258 and the winding of R2 l8 to battery. When thus energized, the control relay R2I8 operates to com- R248. The hold relay R248 being of the slow-torelease type. does not immediately restore, incident to the restoration of the line relay R238, and is retained in its operatedposition due to the completion of the previously mentioned holding circuit for energizing the winding thereof. Accordingly, ground potential is notremoved from the control conductor CH! of the trunk line I18 at this time.

Shortly thereafter and at the beginning of a code ringing cycle, ground potential is applied in the ringing machine to the ring pickup lead C2I5, thereby to complete a circuit for energizing the winding of the switch-through relay R228, this circuit extending from the grounded ring pickup lead C2I5 by way of the contacts 2I3 and 224 and the winding of R228 to battery. When thus energized, the switch-through relay operates to complete, at the contacts 223, a holding circuit for energizing the winding thereof, this circuit extending from groundby way of the contacts 2I2 and 223 and the winding of R228 to battery. Also,

the switch-through relay prepares, at the contacts 222 and 225, points in a circuit traced hereinafter for projecting ringing current from the ringing machine associated with the trunk 285" by way'of the operated reverting callswitch 288, the trunk line I18 and the link I88 over the subscriber line I58, the exact circuit for projecting ringing current from the ringing machine associated with the trunk 285' over the subscriber line I58, depending upon the positiors of the wipers of the minor switches 288 and 288, in a manner more fully described subsequently.

As previously noted, a divided ringing circuit is employed in the system, a'flrst group of substations associated with each party subscriber line having ringers thereat connected between one line conductor of the party line and ground, ,and a second group of substations associated with each party subscriber line having ringers thereat connected between the other line con-' 'ductor of the party line and ground. Accordingly, the operation of the reverting call switch 285 depends upon whether the calling and called substations A and B are in the same group. In the event the substations A and B are in the same group, the reverting call switch 288 operates to cause ringing current of the code corresponding to the. called substation B to be projected over the line conductor of the subscriber line I58 to which the 'ringers at each of the substations A and B are connected. On the other hand, in the event the substations A and B are in different groups, the reverting call switch 288 operates first to cause ringing current 'of the code corresponding to the called substation B to be projected over the line conductor of the subscriber line I58 to which the ringer at the called substation B is connected, and then to cause ringing current of the code corresponding to the calling substation A to be projected over the line conductor of the subscriber line I58 to which the ringer at the calling substation A is connected. Also, it is noted that the substations associated with the subscriber line I58 and having ringers connected to one line conductor thereof are assigned directory numbers comprising a third odd digit; and the substations associated with the subscriber line I58 and having ringers connected to the other line conductor thereof are assigned directory numbers comprising a third even digit.

- Assuming that the third digit of the directory number-o1 the calling substation A is the No. 1, and the third digit of the directory number of the called substation B is the No. 3, the wipers noted of the minorswitch 280 engage the first contacts in the associated contact banks, and the wipers noted of the minor switch 290 engage the third contacts in the associated contact banks. At this time, a circuit is completed for projecting ringing current of the code corresponding to the called substation B over the subscriber line I 50, this circuit extending from the ungrounded terminal of the ringing machinewinding by way of the ringing conductor M3, the third contact in'the contact bank 294 and the associated wiper 293 of the minor switch 290, the I trunk linev I10, and therefrom by way of theoperated link I00, the line conductor CII of the subscriber line I50, and a condenser and the ringer at the called substation B to ground. Also, a circuit is prepared for energizing the upper winding of thering cutoff relay R255 which is completed when the subscriber at the substation B answers the call by removing the receiver of the telephone instrumentthereat from itsiassociated switchhook, this circuit extending, when completed, by way of the previously traced path to the line conductor CI5I of the subscriber line I50, and therefrom by way of the bridge path at the substation B between the line conductors CI5I and CI52 of the subscriber line I50, the line conductor CI52' of the subscriber line I50, the operated link I00, the line conductor CI13 of the trunk line I10, the contacts 225 and the windings 202-and 203 of the transformer 20I to ground.

Assuming that the third dig-it of the directory number of the calling substation A is the No. 2

and the third digit of the directory number of the called substation B is the No.. 4, the wipers noted of the minor switch 280 engage the second contacts in the associated contact banks, and the wipers noted of the minor switch 290 engage the fourth contacts in the associated contact banks. At this time, a circuitis completed for projecting ringing current of the code corresponding to the called substation B over the subscriber line I 50, this circuit extending from the ungrounded terminal of the ringing machine winding by way of the ringing conductor M4, the fourth contact in the contact bank 290'and the associated wiper 295 of the minor switch 290, the windings 205 and 204 of the transformer 20I and the contacts 221 to ground. The ringing current traversing the windings 204 and 205 of the transformer 20I induces a correspondingringing current in thewindings 202 and 203 thereof, which traverses a path extending from ground by way of the windings 203 and 2020f the transformer 20l, and the contacts 225 to the line conductor CI13-of the trunk line I; and therefrom by way of the operated link I00, the line conductor CI52 of the subscr ber line I50 and the condenser and the ringer at the called substation B to ground. Also, a circuit is prepared for energizing the upper winding of the cutoff relay R255 which is completed when tlze subscriber at the called substation B answers the call by removing the receiver of the telephone hook, this circuit extending, when completed, from battery by way of the resistor 201, the

, second contact in the contact bank 284 andthe operated linkI00 to the line conductor C I5I of the subscriber line I and therefrom by way of the bridge path at the substation B between the line conductors CI5I and CI52 of the subscriber line I50 and-a portion of the previously traced circuit to ground at the winding 203 of the transformer 20I. ,7

Assuming that the third digit of the directory number of the calling substation A is the No. 1 and the third digit -of the directory number of the called substation B is the No. 2, the wipers noted of the minor switch 280 engage the first contacts in the associated contact banks, and the wipers noted of the minor switch290 engage the second contacts in the associated contactbanks, At this time, a circuit is completed for projecting ringing current of the code corresponding to the called substation B over "the subscriber line I50, this circuit extending from the ungrounded terminal of the ringing machine winding by way of the ringing conductor. M2, the second contact in the contact bank 296 and the associated wiper 295 of the minor switch 290, the windings-205 and 204 of the transformer 206 and the contacts 221 to ground. This ringing current traversing the windings 204 and 205 of the transformer 20I induces a correspondin ringing current in the windings 202 and 203 thereof which is projected byway of the previouslytraced path over the line conductor CI5I of the subscriber line I50 to ground at the ringer at the called substation B. Also, a'circuit is completed for projecting ringing current of the; code corresponding to the calling substation A over the subscriber line I50, this circuit extending from the ungrounded terminal of the ringing machine by way of the ringing-conductor MI.

the first contact in the contact bank 284 and the associated wiper 283 of the minor switch 280, the second contact in the contact bank 294 and the associated wiper 293 of the minor switch 290, the upper winding of the ring cutoff relay substation A to ground. The ringing machine instrument thereat from its associated switch-- I operates to complete the circuits for applying ringing voltages to the ringing conductors MI to' M5, inclusive, sequentially, thereby to cause the ringer at the called substation B and the ringer at the calling substation A to be operated alternatively. Also, a circuit is prepared for energizirg the upper winding of the ring cutofi relay R255, whichis completed when the subscriber at the substation B answers the call by removing the receiver of the telephone instrument thereat from its associated switchhook, this circuit extending, when completed, from the ringing conductor MI by way of the previously traced path to ground at the winding 203 of the transformer 20I.

Assuming that thethird digit of the directory number of the calling substation A is the No. 2 and the third digit of the directory number of the called substation B is the No. 1, the wipers noted of the minor switch 280 engage the second contacts in the associated contact banks and the wipers noted of the minor switch 290 engage the first contacts in the associated contact banks. At this time, a circuit is completed for projecting ringing current of thecode corresponding to the called substation B over the subscriber line I50, this circuit extending from the ungrounded terminal of the ringing ma-' the ringing conductor M2, the second contact in the contact bank 285 and the associated wiper 285 of the minor switch 250, the first contact in the contact bank 295 and the associated wiper 295 of the minor switch 290, the windings 205 and 204 of the transformer I and the contacts 221 to ground. This ringing current traversing the windings 204 and 205 of the transformer 20I inl sitions.

duces a corresponding ringing current in the so windings 202 and 203 thereof, which is projected by way of the previously traced circuit including the line conductor CI52 of the subscriber line I50 to ground at vthe ringer at the calling substation A. As previously noted, the ringers at the called, and calling substations B and A, respeetively, are operated alternatively.

ing of the ring cutoif rela R255 which is completed when the subscriber at the substation B answers the call by removing the receiver of the telephone instrument thereat from its associated switchhook, this-circuit extending,,when completed, from the ringing conductor MI by way of the previously traced path to ground at the winding 203 of the transformer 20I.

When'the subscriber at the called substation B answers the call, one of the previously traced circuits for energizing the upper winding of the ring cutoff relay R255 is completed, depending upon whether the calling and called substations I A and B, respectively, are in the same or different groups, as previously noted. When thus energized, the ring cutofl relay R255 operates to complete, at the contacts 251, an obvious holding circuit for energizing the lower winding thereof, to interrupt, at the contacts 255, the previously traced path for applying ground potential to the control conductor CI12 of the trunk line I10, and to interrupt, at the contacts 250, the previously traced circuit for energizing the winding of the control relay R2I0, thereby to cause the latter relay to restore, Upon restoring, the control relay R2I0 interrupts, at the contacts 2, the previously traced path for applying at the contacts 245, a circuit for energizing the release magnet M238 of the minor switch 290, this circuit extending from ground by way of the contacts 245 and 264 and the release magnet M239 to battery. When thus energized, the release magnet M239 operates to release the wipers noted of the minor switch 290, thereby to cause these wipers to be returned to their normal po- When the wipers noted of the minor switch 290 are returned to their normal positions, the set of switch springs S235 is actuated into disengagement, thereby to interrupt the previously mentioned holding circuit forenergizing 'the winding of the transfer relay R250, wheregizing the release magnet M239, and completes,

at the contacts 255. a circuit for energizing the release magnet M231, this circuit extending from ground by way of the contacts 245, 255 and 215 and the release magnet M231 to battery. When Also, a circuit is prepared for energizing the upper windground potential'to the ringing machine start lead C206 in order to arrest further operation of the ringing machine associated with the reverting call switch 200, and interrupts, at the contacts 2I2, the previously traced holding circuit for energizing the winding of the switchthrough relay R220 in order to cause the latter relay to restore. Also, the control relay R2I0 interrupts, at the contacts 2, the previously mentioned holding circuit for energizing the winding of the hold relay R240, thereby to cause latter relay to restore shortly thereafter, the

ring cutoff relay R255 being of the slow-to-release type. Also, the hold relay R240 completes.

thus energized, the release magnet M231 operates to release the wipers noted of the minor switch 280, thereby to cause these wipers to be returned to. their normal positions. When the wipers noted of the minor switch 200 are returned to their normal positions the set of switch springs S234 is actuated into disengagement, thereby to interrupt the previously mentioned holding circuit for energizing the winding of the transfer relay R210, whereupon the latter relay restores. Upon restoring, the transfer relay R210 interrupts, at the contacts 215, the pre-- viously traced circuit for energizing the release magnet M231. Upon restoring, the hold relay R240, the ring cutofl' relay R255 and the transfer relay R210 complete, at the contacts'24l, 255 and 2', respectively, thepreviously traced path for applying battery potential by way of the resistor 205 to the control conductor CI12 of the trunk line I10, thereby to mark this trunk line as idle to the connectors of the links having access thereto. switch 200 is completely released for further use.

As previously explained, when the ring cutoif relay R255 in the reverting call-switch 200 operates, ground potential is removed from the control conductor. CI12 of the trunk line I10, thereby to cause the operated link I00 to be released, whereupon the previously traced circuit for energizing in series the lower winding of the line relay RI20 and the upper winding of the cutoff relay RI I0 in the linecircuit I04 individually associated with the subscriber line I54 is interrupted. The line relay RI20 immediately restores to complete, at the contacts I22 and I24, a bridge circuit for energizing in series the upper and lower windings of the cutoff relay RI I0, and to interrupt, at the contacts I23, the previously traced priming circuit for energizing in series the upper and lower windings of the cutoff relay RI III. The bridge circuit for energizing in series the upper and lower windings of the cutofl relay RIIO extends from ground by way of the lower winding of RI I0 and the contacts I24 to the line conductor CI52 of the subscriber line I50, and from battery by way of 'the upper winding of RI I0 and the contacts I22 and H2 to the line conductor CI5I of the subscriber line I 50, a bridge connection being completed at the called substation B between the line con-.

ductors CI5I and CI52 of the subscriber line I50. Accordingly, the cutoff relay RI I0 remains in its operated position incident to the release At this time, the reverting call of the link I when the subscriber at the called substation B answers the reverting call-upon the subscriber line I50. Also, upon restoring, the

an alternative path for applying ground potential to the control conductor CI54 of the subscriber line I50, thereby to mark the subscriber line I50 as busy to the connector switches of the links having access thereto. This path extends from ground by way of the contacts H0 and I26 to the control conductor CI54. Accordingly, at this time, the line circuit IO I individually associated with the subscriber line I50 is operated positively to lock the subscriber line I50 out of service; and talking battery is supplied by way of the previously traced bridge circuit to the telephone instrument at the called substation B.

As previously noted, when the subscriber at the called substation B answers the reverting call on the subscriber line I50, the reverting call switch 200 is released,'thereby to interrupt the circuit for projecting ringing current over the subscriber line I50 in order to cause further operation of the ringer at the calling substation A to be arrested. When the operation of the ringer at the calling substation A is arrested the subscriber thereat is advised that the subscriber at the called substation B hasanswered the re verting call. The subscriber at the substation A then removes the receiver of the telephone instrument thereat from its associated switchhook, thereby to complete an established revertive connection between the calling and called substations A and B, respectively, for two-way communication therebetween, talking batterybeing supplied to the substation A by way of the previouslytraced bridge circuit.

The release of this established connection between the substations A and B is under the control of the last subscriber to replace the receiver of the telephone instrument at his substation upon its associated switchhook. When the last subscriber replaces the receiver of the telephone instrument at his substation upon its associated switchhook, the bridge circuit for energizing in series the upper and lower windings of the cutoff relay RIIO is interrupted, thereby to cause the latter relay to restore. Upon restoring, the cutofi relay RI I0 completes, at the contacts H3,

the previously traced path for applying battery potential by way of the upper winding of the cutoff relay RI I0 and the lower winding of the line relay R120 to the control conductor Cl54 of the subscriber line I50, thereby to mark the subscriber line I50 as idle to the connectors of the links having access thereto.

In view of theabove description of the mode of operation of the apparatus to extend a reverting call from the substation A to the substation B, it will be understood that the apparatus is operative, in a substantially identical manner, to

any one of the subscriber-lines, in which case the connector I02 thereof will not be operated subsequently to seize a line accessible thereto, in

order to cause the operation of the switch through relay therein, whereby ground potential will be removed from the wiper I8 I, as previously noted. Under these conditions, when ground potential is removed from the wiper I8 I the circuit for energizing in series the upper winding of the cutoff relay and the lower winding of the line relay in the line circuit individually associated with the line having the fault thereon is interrupted,thereby to cause the line relay therein to restore and the 'cutofltrelay therein to remain operated. The operated cutoff relay in the line circuit individually associated with the line having the fault thereon causes the last-mentioned line to be locked out of service, in the manner previously explained, in connection with the extension of a reverting call between the substations A and B over the subscriber line I50. When the fault is removed from the line the bridge circuit for energizing in series the upper and lower windings of the cutoff relay'in the line extend a reverting call from the substation B to the substation A, from the substation C to the substation D, and from the substation D to the substation C.

Also, it is noted that a timing arrangement is incorporated in the connector I02 which isoperative in the event the switch-through relay therein does not operate within a predetermined time interval, due to the fact that the connector has not been fully operated to seize a line accessible thereto, to cause ground potential to be removed from the wiper II. For example, the link I00 may be seized, in the previously described manner, by the appearance of a fault on circuit individually associated therewith is interrupted, thereby to cause the cutoff relay to restore, whereupon the line is again marked as idle to the connectors of the links having access thereto.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein, and

it is intended to cover in the appended claims all such modifications as fall within the ltru spirit and scope of the invention.

What is claimed is:

1. A line circuit adapted for use in a telephone retaining operated said cutoff relay subsequent to the release of said switching apparatus in the event a call remains on said line, and control circuits for said switching apparatus governed by said line relay and said cutoff relay.

2. A line circuit adapted for use in a telephone system including-a line accessible to automatic switching apparatus; said line circuitcomprising a line relay, a cut-off relay, means responsive to the presence of a call on said line for causing operation of said line relay, means controlled when said line relay is operated and said cutoff relay is restored for marking said line as a calling line to said switching apparatus, means responsive to the seizure of said line when a call is thereon by said switching apparatus for retaining operated said line relay and for causing operation of said cutoff relay, means controlled when said line relay and said cutoff relay are operated for marking said line as a busy called line to said switching apparatus, means responsive to the release of said line by said switching apparatus for causing restoration of said line relay, means for retaining operated said cutofi relay subsequent to the release of said switching apparatus in the event a call remains on said switching apparatus; said line circuit comprising a line relay, a cutofl relay, means responsive to the presence of a call on said line for causing operation of said line relay, means controlled when said line relay is operated and said cutoff relay is restored for marking said line as a calling line to said switching apparatus and for causing said switching apparatus to seize said line, means responsive to the seizure of said line when a call is thereon by said switching apparatus for retaining operated said line relay and for causing operation of said. cutofl relay, means controlled when said line relay and said cutofi! relay are operated for marking said line as a busy called line to said switching apparatus, means for causing said switching apparatus to release said line, means responsive to the release of said line by said switching apparatus for causing restoration of said line relay, means for retaining operated said cutofl relay subsequent to the release of said switching apparatus in the event a call remains on said line, and means controlled when said line relay is restored and said cutoff relay is operated for marking said line as a busy locked-out line to said switching apparatus.

'4. A line circuit adapted for use in a telephone system including a line accessible to automatic switching apparatus; said line circuit comprising a line relay, a cutofl relay, 9. control network including-a series operating circuit for said line relay and said cutoff relay, means for causing said switching apparatus to seize said line as a calling line or as a called line, means controlled when said line is seized by said switching apparatus for completing said series operating circuit, and control circuits for said switching apparatus governed by said line relay and said cutofl relay. 5. A line circuit adapted for use in a telephone system including a subscriber line of the party type and automatic switching apparatus having access to said subscriber line; said line circuit comprising a line relay, a cutoff relay including two windings, a control network for selectively operating said line relay and said cutofl relay, control circuits for said switching apparatus governed by said line relay and said cutofl relay, whereby said switching apparatus is selectively controllable to extend a connection to a substation on said subscriber line and to extend a connection from a substation on said subscriber line and to extend a connection between two substations on said subscriber line, and a circuit including the two windings of said cutofi relay for supplying talking current to the two substations on said subscriber line when a connection is ex-- tended therebetween.

6. A line circuit adapted for use he telephone system including a subscriber lineof the party type and automatic switching apparatus having access to said subscriber line; said line circuit consisting solely of a linerelay, a cutoff relay, said relays being mechanically operative entirely independently of each other, a control network for selectively operating said line relay and said cutoff relay, and control circuits for said switching apparatus governed by said line relay and said cutoff relay, whereby said switching apparatus is selectively controllable to render to the substations on said line both calling and called services and also reverting call service.

7. A line circuit adapted for use in a telephone system including a line accessible to automatic switching apparatus; said line circuit comprising a line relay, a cutoff relay, a control network including a series operating circuit for said line relay and said cutoff relay, and control circuits for said switching apparatus governed by said line relay and said cutoff relay.

8. A line circuit adapted for use in a telephone system including a line accessible to automatic switching apparatus; said line circuit comprising a line relay; a cutofl relay; a control network including a series operating circuit for said linerelay and said cutofi relay, an independent operating circuit for said line relay, and a holding circuit for said cutofl relay; and control circuits for said switching apparatus governed by said line relay and said cutofi relay.

9. A line circuit adapted for use in a telephone system including a line accessible to automatic switching apparatus; said line circuit comprising a line relay including first and second windings;

a cutoff relay including first and second windings; a control network including a first operating circuit including the first winding of said line relay, a second operating circuit including in series the second winding of said line relay and the first winding of said cutoff relay, and a holding circuit including the second winding of said cutofl. relay; and control circuits for said switching apparatus governed by said line relay and said cutofi relay.

10. A line circuit adapted for use in a telephone system including a line accessible to automatic switching apparatus; said line circuit comprising a line relay including first and second windings; a cutoff relay including first and second windings; a control network including a first operating circuit including the first winding of said line relay, a second operating circuit including in series the second winding of said line relay and the first winding of said cutofi relay, and a holding circuit including in series the first and the second windings of said cutoff relay; and control circuits for said switching apparatus governed by said line relay and said cutoff relay.

11. A line circuit adapted for use in a telephone system including a line accessible to automatic switching apparatus; a line relay including a winding; a cutofi relay including two windings; a control network including an operating circuit including the winding of said line relay, and two independent holding circuits each including in series the first and the second windings of said cutoff relay; and control circuits for said switching apparatus governed by said line relay and said cutoff relay.

MORRIS E. GRIFFINS. 

